Abstract: Improved methods of disinfecting and/or preserving contact lenses comprises treating said lenses with an effective concentration of a solution comprising a biguanide or a water soluble salt of the formula: ##STR1## wherein R.sub.1 and R.sub.3 are selected hydrogen, halogen, alkyl, alkoxy, nitro, --SO.sub.2 R.sub.4, carboxyl or hydroxyl where R.sub.4 is --NH.sub.2, --NHR', --NR'R", --OR' or --O--aryl in which R' and R" are alkyl or alkoxy; R.sub.2 is hydrogen or halogen and X is hydrogen or alkyl, provided that when R.sub.2 is halogen then both R.sub.1 and R.sub.3 are hydrogen and X is alkyl. The method provides for disinfecting and/or preserving contact lenses wherein the monomeric biguanide-containing solutions offer a wide spectrum of antimicrobial activity with nominal binding and concentrating onto lens surfaces and low levels of eye tissue irritation or inflammation.